Harriet Harman's plans to extend maternity leave have sparked the predictable hysteria. There's a website called HarrietHarmansucks.com, and her cabinet colleague Lord Mandelson (with whom she reportedly has a chilly relationship) has toned down her initial proposals. Now the new issue of Prospect magazine carries a more nuanced response from LSE academic Catherine Hakim. Added maternity leave would not only be bad for employers and British business, Hakim says, but would actually harm women in work too. "Family-friendly policies have actually been the cause of the glass ceiling for women, not the solution," she writes.

Her case is a persuasive one, and it has gained a lot of currency in the past few months – a recent Daily Mail headline for an article by Vogue editor Alexandra Shulman said it all: "Year-long maternity leave, flexi hours, four day weeks ... why would ANY boss hire a woman?" Far from extending maternity leave (currently anywhere between one to 12 months), we should be cutting it back: this is the only way to make women more equal at work, as it would make them less of a "risky" hire for male employers. Or so the argument goes.

Yet on closer examination, how many of the so-called "negative effects" of generous maternity leave are truly harmful? According to Hakim, evidence that around three-quarters of women who return to work after maternity leave go part-time, or find other flexible terms, is "troubling". Why? Isn't this rather an encouraging sign that a majority of mothers are able to strike a healthy work-life balance? Not all women (or men's) top ambition is to be a chief executive. Plus, Harman's plans do not include compulsory maternity leave: any woman who wants to hop out of her hospital bed and straight back into the office is still free to do so – as she should be.

Gaby Hinsliff's moving account of her decision to quit the Observer underscored just how emotive this subject can be. But one can also level it down to very basic, practical terms. If we cut back on maternity leave, how will working mothers be able to exclusively breast-feed for six months, as the World Health Organisation recommends? Plenty choose not to breast-feed for many good reasons, though surely a mother should at least have this option, with all its proven health benefits, and still be able to keep her job. You could win this side of the argument purely on NHS cost-effectiveness grounds.

Of course every work and domestic situation is unique, and certain jobs can never truly be made family-friendly. But this makes an even stronger case for a change in the law: women are entitled to these "family-unfriendly" jobs too, and so the rules should better accommodate the involvement of both parents in child-rearing. Which is why, laudable though they are, Harman's plans don't go far enough.

In their 2005 manifesto, Labour promised up to six months' paternity leave for all fathers, a proposal they have now backed away from – thanks to, again, alleged interference from the Prince of Darkness. To be fair, surveys carried out in Sweden showed that before a policy of generous paternity leave was introduced a majority of Swedish men and women were against it. But just because a working father doesn't want to be more involved in the day-to-day parenting of a small child, does this mean he should automatically be allowed to opt out? As things stand, women certainly can't. And surely, if employment laws are to have any point at all, they should discourage reductive gender roles. (A majority of Swedish women may have been against mandatory leave before it was introduced, but I wonder how many object to it now.) Plus, as Richard Reeves has pointed out in the Observer, there are plenty of British fathers who do crave more time with their children and a fairer allocation of parenting options.

One of the things that happen all too often in this debate is that men are reduced to boorish, irresponsible stereotypes – often by well-intending women arguing passionately for equality. Harriet Harman is right to push for more generous maternity leave for those who want it. But it should not be only women in pursuit of that elusive goal of "having it all". Men deserve a shot at it too.